As voters head to the polls across the United States next Tuesday, the results from some states will be watched more closely than others.

Under the U.S. election system, the presidency is determined not by who receives the most votes nationwide but by who captures the most number of weighted votes assigned to each state. Ten swing states, where the outcome is not a foregone conclusion, provide the key to reaching the 270 votes in the country’s electoral college needed to win the presidency.

COLORADO

The state in the mountainous western United States was a longtime Republican stronghold until President Barack Obama won Colorado’s nine electoral votes in 2008. Democrats control the state’s congressional delegations and serve as governor, but Mitt Romney has a slight edge in opinion polls in the state. He could benefit from a strong, usually Republican-leaning, evangelical Christian community as well as anti-government sentiment in the state.

FLORIDA

The largest swing state with 29 electoral college votes, Florida’s importance was demonstrated most dramatically in the 2000 election that saw a small margin of votes in the state hand the presidency to Republican George W. Bush instead of Democrat Al Gore.

The southern sun has lured many retirees to the state, so proposals about health care for seniors and pensions are particularly hot topics for candidates. The state’s large Hispanic population could also be key, with Mr. Obama seeking to woo the key voting bloc even as many older Cuban-American tend to vote Republican. Mr. Obama carried the state in 2008, but the candidates are tied in recent polls.

IOWA

The central state of Iowa has just six electoral votes, but receives an unusual amount of attention from candidates in part because of its key first-in-the-nation vote during the primary season that prompts most politicians to launch their campaigns there. Mr. Obama leads in polls, but recent contests have shown the state to be narrowly divided.

NORTH CAROLINA

The southern state, with 15 electoral votes, favours Mr. Romney with its many socially conservative voters. Mr. Obama narrowly won the state, with its large African American population, in 2008, but opinion polls show Mr. Romney leading this time around.

NEW HAMPSHIRE

The small north-eastern state, like its Midwestern cousin Iowa, pulls above its weight politically despite having just four electoral votes. The state held the campaign season’s first true primary contest in January and both candidates have spent considerable time here. Mr. Romney owns a summer home in the state and was the governor of neighbouring Massachusetts, but Mr. Obama crushed Republican John McCain by a large margin in 2008.

NEVADA

The desert western state with six electoral votes was hard hit by the financial crisis, witnessing a wave of home foreclosures and unemployment far above the national average. Some 12.1 per cent of Nevadans were unemployed in August, and dissatisfaction with the economy could help Mr. Romney. However, the state’s large Hispanic population pushed the state into Mr. Obama’s column in 2008 and could help him again.

PENNSYLVANIA

The north-eastern state brings the winner a nice haul of 20 electoral votes, but has not given them to a Republican since 1988. Though the state leans Democratic, it has been competitive with narrow margins in recent elections. The large cities of Philadelphia and Pittsburgh are strongholds for Mr. Obama, but the central rural part of the state could bring many votes to Mr. Romney.

OHIO

The key state of Ohio mirrors the United States at large with its mix of cities, suburbs and rural areas. No Republican has ever won the White House without its 18 electoral votes and no candidate — Democrat or Republican — since John F Kennedy in 1960 has lost it and still become president. Both Mr. Obama and Mr. Romney have spent considerable time here in recent weeks and have substantial get-out-the-vote efforts.

VIRGINIA

The state with 13 electoral votes was a key part of Obama’s victory in 2008 and had not supported a Democratic candidate since 1964. The state’s northern suburbs outside US capital Washington have made Virginia more competitive with a more Democratic electorate than more conservative rural parts of the state.

WISCONSIN

The north central state of Wisconsin holds 10 electoral college votes and has been a Democratic prize in recent elections. But Mr. Romney’s vice presidential candidate, Paul Ryan, hails from the state and a conservative uprising over union rights that saw the state’s Republican governor survive a recall election earlier this year could mean the state is now more competitive.

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